The present invention is directed to an apparatus for compressing breast tissue during diagnostic procedures and which contains an element that may be removed to permit access to the breast for biopsy. In addition, the invention encompasses improved diagnostic procedures that make use of this apparatus.
During routine mammographic procedures, breast tissue is compressed in order to obtain higher quality images. Typically, a flat, rigid surface is used to maintain uniform pressure on the breast (see e.g., U.S. Pat. Nos. 4,090,084; 3,578,971; and 3,973,126), but devices having curved surfaces or rounded ridges have also been used (see e.g., U.S. Pat. Nos. 3,971,950; 4,962,515). If an abnormality appears on a mammogram, a needle biopsy is often performed to determine whether the lesion observed is cancerous.
Needle biopsies of breast tissue normally take place in two stages. In the first part of the procedure, an imaging technique is performed in order to accurately target the abnormality. Breast tissue is again compressed to improve resolution, but the device used must permit subsequent access to the breast for needle insertion. Thus, compression devices typically have either an opening or a section with perforations (see, e.g., U.S. Pat. No. 4,691,333). Unfortunately, both of these types of devices have undesirable features. Devices with an opening or xe2x80x9cwindowxe2x80x9d create an uneven pressure during imaging and poorer resolution pictures. Devices with perforations may also cause uneven pressure (albeit to a lesser degree) and may limit access to the breast. Ideally, a compression device should generate uniform pressure for imaging but subsequently allow access to the breast for needle placement while maintaining tissue in an immobilized state.
In its first aspect, the present invention is directed to an apparatus that can be used for compressing breast tissue during a diagnostic imaging technique or needle biopsy. The apparatus has two distinct plates. There is a planar bottom plate containing a smaller open region, or xe2x80x9cwindow,xe2x80x9d that can be localized over the breast. In addition, there is a planar top plate that is designed to fit over and make substantially even contact with the bottom plate. The top plate has a raised element that corresponds to and fits inside the window of the bottom plate. This raised element should be of a thickness such that when the two plates make contact, the window in the bottom plate is filled to form an essentially flat lower surface for contacting breast tissue. Thus, the raised element should be elevated to the thickness of the bottom plate. For example, if the bottom plate were 3 mm thick, the raised element should be elevated approximately 3 mm above the plane of the top plate. The insertion of the raised element into the opening of the bottom plate should not result in a gap of greater than about 0.2 cm on any one side. For example, if the opening in the bottom plate were 4 cm by 8 cm, the raised region element of the top plate should typically have dimensions of about 3.9 cm by 7.9 cm.
In addition, the apparatus contains means for holding the top and bottom plates together with sufficient force to prevent the plates from separating when the apparatus is used diagnostically to compress breast tissue, i.e., the lower surface of the bottom plate should remain substantially flat during the diagnostic procedure. In most cases, the opening in the bottom plate will have a grid along its edges to aid in needle placement during biopsy. For example, one edge of the opening may contain a series of numbers while a second edge running perpendicular to the first has a series of letters.
The particular means for holding plates together is not critical to the invention. Screws may be inserted or the two plates may simply be held in place with clamps. In one design, the bottom plate has a substantially perpendicular end piece along at least two opposing ends that the top plate will fit between. These end pieces may have holes for the insertion of screws that also enter corresponding holes in the top plate and hold it in place. Alternatively, the top plate may have substantially perpendicular end pieces with holes for screws. These holes are aligned with corresponding holes in an endwall running along the sides of, and perpendicular to, the bottom plate. Screws are inserted through the two sets of holes to hold the plates together. In addition, the anterior edge of the top plate is slid under a reinforcing piece attached to the anterior endwall of the bottom plate to prevent the upward displacement of the top plate during breast compression procedures.
In a second aspect, the invention is directed to an improved method for compressing breast tissue during needle biopsy by applying pressure using an apparatus with a removable member. The removable member fills an opening in the apparatus to form a flat surface for contacting breast tissue. It is then removed, without repositioning the breast, to form an open region for needle placement during biopsy. Preferably, the apparatus will correspond to one described above.
The invention also encompasses an improved method for diagnostically examining breast tissue for a cancerous lesion. The method entails performing an imaging procedure in which breast tissue is compressed with an apparatus having a flat, planar lower surface with a removable member in contact with the breast undergoing examination. The removable member is then withdrawn without moving the breast in order to form an opening for performing a needle biopsy. Again, it is preferred that an apparatus as described above be used in the method.